Semiconductor device fabrication is the process used to create integrated circuits present in everyday electrical and electronic devices. In general, semiconductor device fabrication is a multiple-step sequence of photographic and chemical processing steps during which electronic circuits are gradually created on a wafer made of semiconducting material. Virtually every step of semiconductor device fabrication is continually evolving in an effort to obtain increased efficiencies and cost savings.
Surface grinding or polishing operations in semiconductor device fabrication can entail back grinding and face grinding. Wafer back grinding is a process in semiconductor device fabrication in which the backside of a wafer is ground to the correct wafer thickness prior to assembly. It is also referred to as “wafer thinning.” Wafer back grinding is indispensable to meet dimensional requirements of decreasing semiconductor thinness. Wafer face grinding is a process in semiconductor device fabrication in which the front or active surface of the wafer is planarized, or flattened, after each layer is formed on the substrate in order to meet exceedingly stringent flatness requirements necessary for small-dimensioned patterning. Back grinding and face grinding operations, collectively referred to herein as surface grinding, have been implemented in various forms on existing machines.
Referring to FIGS. 1 and 2, FIG. 1 shows a partial perspective view of a prior art surface grinding apparatus 20, and FIG. 2 shows an illustration of a partial top view of surface grinding apparatus 20. Surface grinding apparatus 20 may be utilized to perform back grinding and/or face grinding on workpieces such as semiconductor and high-precision wafers and substrates including, for example, silicon, gallium arsenide, silicon carbide, sapphire, quartz, fused silica, glass, layered silicon-insulator-silicon substrate, and so forth.
Surface grinding apparatus 20 is adapted to concurrently process two workpieces. Accordingly, surface grinding apparatus 20 includes a first (i.e., right) grind chamber 22 and a second (i.e., left) grind chamber 24 located in a cabinet 26 of apparatus 20. A first (i.e., right) spindle 28 is positioned in first grind chamber 22, and a second (i.e., left) spindle 30 (visible in FIG. 2) is positioned in second grind chamber 24. Each of first and second spindles 28 and 30, respectively, is capable of holding a workpiece while performing surface grinding. First and second spindles 28 and 30 may also be referred to as wafer spindles, wafer chucks, or simply chucks.
A mounting plate 32 is coupled to a top surface of cabinet 26. Mounting plate 32 includes a first opening 34 and a second opening 36 (visible in FIG. 2). A first mounting section 38 in mounting plate 32 encircles first opening 34. Likewise, a second mounting section 40 in mounting plate 32 encircles second opening 36. A first grind seal 42 resides in first mounting section 38 and a second grind seal 44 resides in second mounting section 40. Each of first and second grind seals 42 and 44, respectively, is formed as a continuous ring that is substantially oval in shape so as to fit in their corresponding first and second mounting sections 38 and 40.
Surface grind apparatus 20 further includes a first grinding wheel 46 and a second grinding wheel 48, represented in FIG. 2. First and second grinding wheels 46 and 48 extend through a sealing plate 50 and may be vertically adjusted to reside in either of first and second grind chambers 22 and 24, respectively. Coolant nozzles 52 (of which only one is visible) are positioned in each of first and second grind chambers 22 and 24 to direct water onto first and second grinding wheels 46 and 48 and workpieces (not shown) on first and second spindles 28 and 30 during grinding.
Each of first and second grinding wheels 46 and 48, respectively, is attached to a separate grind spindle 54, of which only one is visible in FIG. 1, and grind spindles 54 are coupled to a bridge element 56. In general, corresponding rotational axes of first and second grinding wheels 46 and 48 are laterally displaced (i.e., separated) from one another by a fixed distance 58, e.g., fifteen inches. Likewise, corresponding centers of first and second spindles 28 and 30 are laterally displaced (i.e., separated) from one another by a fixed distance 60, e.g., fifteen inches. However, bridge element 56 controls the linear position, or translation, of first grinding wheel 46, second grinding wheel 48, and sealing plate 50 relative to first and second spindles 28 and 30, respectively. Accordingly, first grinding wheel 46, second grinding wheel 48, and sealing plate 50 can be directed to move laterally relative to first and second spindles 28 and 30 to suitable positions (discussed below) for surface grinding operations.
First and second grind seals 42 and 44 are inflatable seals. Accordingly, first and second grind seals 42 and 44 can be deflated to enable unencumbered movement of sealing plate 50 as sealing plate 50 moves across mounting plate 32. However, when sealing plate 50 is moved into a grinding position covering one or both of first and second grind chambers 22 and 24, one or both of first and second grind seals 42 and 44 are inflated in order to contain water and effluent while grinding.
FIG. 3 shows a chart 62 representing surface grinding positions in which the prior art surface grinding apparatus 20 (FIG. 1) can be placed. In particular, FIG. 3 shows a position of first and second grinding wheels 46 and 48, respectively, relative to first and second spindles 28 and 30, respectively. The surface grinding positions include a first, e.g., right, surface grinding position 64, a second, e.g., center, surface grinding position 66, and a third, e.g., left surface grinding position 68. In this example, the surface grinding positions are referenced from first grinding position 64. That is, bridge element 56 (FIG. 1) is “homed” by translating bridge element 56 the full distance to a right side limit switch, then bridge element 56 is translated leftward to first grinding position 64, which is considered “home.” Second and third surface grinding positions 66 and 68, respectively, are defined as a distance from first surface grinding position 64 (e.g., 15.8 inches and 31.63 inches, respectively) as shown in chart 62.
Surface grinding apparatus 20 may be configured to perform a two-step grinding process. In an example, surface grinding apparatus 20 may be capable of carrying out coarse and fine grinding on a first workpiece 70 and a second workpiece 72. To that end, first grinding wheel 46 may be a fine grinding wheel, as demarcated by “FINE,” and second grinding wheel 48 may be a coarse grinding wheel, as demarcated by “COARSE.” First and second workpieces 70 and 72 are represented in FIG. 3 by shading in order to distinguish them from the underlying first and second spindles 28 and 30, respectively. Additionally, although the portion of each of spindles 28 and 30 underlying first and second grinding wheels 46 and 48 is represented in ghost form by dashed lines, the portion of each of first and second workpieces 70 and 72, respectively, underlying first and second grinding wheels 46 an 48 is not shown for simplicity of illustration.
A two-step grinding process may entail placing first workpiece 70 on first spindle 28 and placing second workpiece 72 on second spindle 30. Of course, placement of first and second workpieces 70 and 72 on first and second spindles 28 and 30 can be performed through automated placement by a robot apparatus (not shown) and first and second workpieces 70 and 72 may be retained on first and spindles 28 and 30 by conventional means so they do not slip or otherwise move. A sequence of grinding operations can include adjusting first and second grinding wheels 46 and 48 to first surface grinding position 64 so that first grinding wheel 46 is idle and second grinding wheel 48 performs coarse grinding on the surface of first workpiece 70. Next, first and second grinding wheels 46 and 48 can be adjusted to second surface grinding position 66 so first grinding wheel 46 performs fine grinding on first workpiece 70 and second grinding wheel 48 concurrently performs coarse grinding on second workpiece 72. Finally, first and second grinding wheels 46 and 48 can be adjusted to third surface grinding position 68 so first grinding wheel 46 performs fine grinding on second workpiece 72 and second grinding wheel 48 is idle. In any of grinding positions 64, 66, and 68, either or both of first and second grinding wheels, and either or both of first and second spindles will rotate during surface grinding.
Surface grinding apparatus 20 may achieve increased efficiency of grinding over devices with single grind wheels and single grind chucks. However, an even greater increase in wafer conditioning efficiency can lower the cost of semiconductor devices through decreases in manufacturing costs and equipment costs.